I ordered a meal from McDonalds once and paid with a £5 note. I wasn't paying attention at the time and got given £5, plus the regular change. I didn't realise what had happened until I walked out. More people should do that.

Otherwise, I'd had meals screwed up before but only when I've eaten in. When going to the drive-through we've often ended up with an extra drink or something. I bought a cheeseburger the other day though and they didn't do it without the gerkin, onion, mustard and ketchup like I asked. I don't actually dislike any of those except for the gerkin and the mustard, but they're just nicer without.

Edit: I suppose it would also worth bearing that I went into Subway for my lunch the other day and ordered a veggie delite (which is all I ever order when I go to Subway once in a blue moon). They got to the meat bit and asked if I wanted any cheese or my bread toasting. I said no. They took me over to the salad bit, with my empty, sliced roll and asked if I wanted salad. I was tempted to say "no" just to see what they'd do.